The present invention refers to a plate package for a plate heat exchanger, which package includes a plurality of heat exchanger plates, which are stacked on each other and which each includes a number of portholes, wherein the plates are compression moulded and permanently connected to each other in a number of joints in such a manner that the plates between each other form a first passage for a first fluid and a second passage for a second fluid, wherein the plate package is designed to permit at least one of said fluids to flow through the respective passages at a predetermined maximum working pressure. The invention also refers to a method for manufacturing a plate package for a plate heat exchanger, which package includes a plurality of heat exchanger plates, which are stacked on each other and which each includes a number of portholes, wherein the plates are compression moulded in such a manner that the plates in the plate package between each other form a first passage for a first fluid and a second passage for a second fluid and wherein the plate package is designed to permit at least one of said fluids to flow through the respective passages at a predetermined working pressure. Furthermore, the invention refers to a use of a plate package, and a plate heat exchanger.
Such plate packages are used in plate& heat exchangers for a plurality of various applications. The plates are normally manufactured in stainless steel and permanently connected to each other by brazing. As braze material copper is normally used. Such plate packages and plate heat exchangers have very high explosion pressures, i.e. they withstand very high inner pressures in one or several of the passages without braking of the plate package. The high explosion pressures are achieved thanks to the high ductility of the used materials and the capability of the materials to obtain a high yield limit through cold working. The explosion pressure may also be increased by increasing the sheet thickness of the heat exchanger plates, the pressure plate and the frame plate.
There is of course a general interest of increasing the strength of such plate packages. In addition, in such plate packages, a certain spread in the pressure fatigue quality arises since the permanent connection between adjacent plates in certain joints could be defect or possible be partly missing. During use of a plate package in a heat exchanger, the plate package is frequently subjected to pulsating pressure, wherein the highest pressure pulses define, and are not permitted to exceed, the highest permitted working pressure. These high pressure pulses lead to high stresses in such defect joints and in joints around defect joints or around areas where the joints are partly missing for any reason. High stresses are of course also present in all highly loaded areas even if the joints are free from defects.
During the manufacture of such plate packages, a pressure test of the plate package takes place today before delivery thereof. Such a pressure test typically takes place at a test pressure corresponding to 1,3-1,8× the maximum working pressure depending on pressure vessel code, operation conditions, i. e. the strength of the material at the designed temperature in relation to the strength at the test pressure temperature. If the plate package withstands this pressure, the quality is regarded to be sufficient. The test pressure level is such that it does not give rise to any visible or measurable plastic deformation of the materials in the-plate package.
U.S. Pat. No. 3,458,917 discloses a way of manufacturing another type of plate heat exchanger. Two substantially plane plates are laid adjacent to each other and joined to each other at point- or line-shaped weld joints. Thereafter a deformation pressure is supplied by the supply of a pressurised medium to the interspace between adjacent plates. The deformation pressure is such that the plates will be deformed and obtain a wavy shape. In such a way, the desired passage between the plates is created.